/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.ui.context.support;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.context.HierarchicalMessageSource;
import org.springframework.context.MessageSource;
import org.springframework.context.support.ResourceBundleMessageSource;
import org.springframework.lang.Nullable;
import org.springframework.ui.context.HierarchicalThemeSource;
import org.springframework.ui.context.Theme;
import org.springframework.ui.context.ThemeSource;

/**
 * {@link ThemeSource} implementation that looks up an individual
 * {@link java.util.ResourceBundle} per theme. The theme name gets
 * interpreted as ResourceBundle basename, supporting a common
 * basename prefix for all themes.
 *
 * @author Jean-Pierre Pawlak
 * @author Juergen Hoeller
 * @see #setBasenamePrefix
 * @see java.util.ResourceBundle
 * @see org.springframework.context.support.ResourceBundleMessageSource
 */
public class ResourceBundleThemeSource implements HierarchicalThemeSource, BeanClassLoaderAware {

    protected final Log logger = LogFactory.getLog(getClass());

    @Nullable
    private ThemeSource parentThemeSource;

    private String basenamePrefix = "";

    @Nullable
    private String defaultEncoding;

    @Nullable
    private Boolean fallbackToSystemLocale;

    @Nullable
    private ClassLoader beanClassLoader;

    /**
     * Map from theme name to Theme instance.
     */
    private final Map<String, Theme> themeCache = new ConcurrentHashMap<>();


    @Override
    public void setParentThemeSource(@Nullable ThemeSource parent) {
        this.parentThemeSource = parent;

        // Update existing Theme objects.
        // Usually there shouldn't be any at the time of this call.
        synchronized (this.themeCache) {
            for (Theme theme : this.themeCache.values()) {
                initParent(theme);
            }
        }
    }

    @Override
    @Nullable
    public ThemeSource getParentThemeSource() {
        return this.parentThemeSource;
    }

    /**
     * Set the prefix that gets applied to the ResourceBundle basenames,
     * i.e. the theme names.
     * E.g.: basenamePrefix="test.", themeName="theme" -> basename="test.theme".
     * <p>Note that ResourceBundle names are effectively classpath locations: As a
     * consequence, the JDK's standard ResourceBundle treats dots as package separators.
     * This means that "test.theme" is effectively equivalent to "test/theme",
     * just like it is for programmatic {@code java.util.ResourceBundle} usage.
     *
     * @see java.util.ResourceBundle#getBundle(String)
     */
    public void setBasenamePrefix(@Nullable String basenamePrefix) {
        this.basenamePrefix = (basenamePrefix != null ? basenamePrefix : "");
    }

    /**
     * Set the default charset to use for parsing resource bundle files.
     * <p>{@link ResourceBundleMessageSource}'s default is the
     * {@code java.util.ResourceBundle} default encoding: ISO-8859-1.
     *
     * @see ResourceBundleMessageSource#setDefaultEncoding
     * @since 4.2
     */
    public void setDefaultEncoding(@Nullable String defaultEncoding) {
        this.defaultEncoding = defaultEncoding;
    }

    /**
     * Set whether to fall back to the system Locale if no files for a
     * specific Locale have been found.
     * <p>{@link ResourceBundleMessageSource}'s default is "true".
     *
     * @see ResourceBundleMessageSource#setFallbackToSystemLocale
     * @since 4.2
     */
    public void setFallbackToSystemLocale(boolean fallbackToSystemLocale) {
        this.fallbackToSystemLocale = fallbackToSystemLocale;
    }

    @Override
    public void setBeanClassLoader(@Nullable ClassLoader beanClassLoader) {
        this.beanClassLoader = beanClassLoader;
    }


    /**
     * This implementation returns a SimpleTheme instance, holding a
     * ResourceBundle-based MessageSource whose basename corresponds to
     * the given theme name (prefixed by the configured "basenamePrefix").
     * <p>SimpleTheme instances are cached per theme name. Use a reloadable
     * MessageSource if themes should reflect changes to the underlying files.
     *
     * @see #setBasenamePrefix
     * @see #createMessageSource
     */
    @Override
    @Nullable
    public Theme getTheme(String themeName) {
        Theme theme = this.themeCache.get(themeName);
        if (theme == null) {
            synchronized (this.themeCache) {
                theme = this.themeCache.get(themeName);
                if (theme == null) {
                    String basename = this.basenamePrefix + themeName;
                    MessageSource messageSource = createMessageSource(basename);
                    theme = new SimpleTheme(themeName, messageSource);
                    initParent(theme);
                    this.themeCache.put(themeName, theme);
                    if (logger.isDebugEnabled()) {
                        logger.debug("Theme created: name '" + themeName + "', basename [" + basename + "]");
                    }
                }
            }
        }
        return theme;
    }

    /**
     * Create a MessageSource for the given basename,
     * to be used as MessageSource for the corresponding theme.
     * <p>Default implementation creates a ResourceBundleMessageSource.
     * for the given basename. A subclass could create a specifically
     * configured ReloadableResourceBundleMessageSource, for example.
     *
     * @param basename the basename to create a MessageSource for
     * @return the MessageSource
     * @see org.springframework.context.support.ResourceBundleMessageSource
     * @see org.springframework.context.support.ReloadableResourceBundleMessageSource
     */
    protected MessageSource createMessageSource(String basename) {
        ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
        messageSource.setBasename(basename);
        if (this.defaultEncoding != null) {
            messageSource.setDefaultEncoding(this.defaultEncoding);
        }
        if (this.fallbackToSystemLocale != null) {
            messageSource.setFallbackToSystemLocale(this.fallbackToSystemLocale);
        }
        if (this.beanClassLoader != null) {
            messageSource.setBeanClassLoader(this.beanClassLoader);
        }
        return messageSource;
    }

    /**
     * Initialize the MessageSource of the given theme with the
     * one from the corresponding parent of this ThemeSource.
     *
     * @param theme the Theme to (re-)initialize
     */
    protected void initParent(Theme theme) {
        if (theme.getMessageSource() instanceof HierarchicalMessageSource) {
            HierarchicalMessageSource messageSource = (HierarchicalMessageSource) theme.getMessageSource();
            if (getParentThemeSource() != null && messageSource.getParentMessageSource() == null) {
                Theme parentTheme = getParentThemeSource().getTheme(theme.getName());
                if (parentTheme != null) {
                    messageSource.setParentMessageSource(parentTheme.getMessageSource());
                }
            }
        }
    }

}
